Victoria state Fire Service Commissioner Craig Lapsley said 37 blazes were burning out of control across the state, threatening rural towns and the fringes of Australia's second largest city, Melbourne.
Homes were lost in Victoria, but authorities had yet to assess the numbers, Country Fire Authority spokeswoman Anushia Sivanesan said.
Lapsley said at least one firefighter was injured. The firefighter was hit by a falling tree and received medical treatment.
According to Lapsley, the fire conditions were at their worst since 2009, when wildfires killed 173 people and destroyed more than 2,000 homes in Victoria in little more than a single day in February.
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In neighboring New South Wales state, the Rural Fire Service reported 50 fires burning, one temporarily closing the Hume Highway, which connects Melbourne with Sydney, Australia's largest city.
There were no immediate reports of homes lost in New South Wales, Australia's most populous state.
Destructive wildfires are a common feature across much of Australia during the summer months.
Temperatures exceeded 40 degrees Celsius (104 Fahrenheit) in parts of Victoria, Australia's second-most populous state, and New South Wales.